Sébastien Horna

Consistency constraints and 3D building reconstruction

Virtual architectural (indoor) scenes are often modeled in 3D for various types of simulation systems. For instance, some authors propose methods dedicated to lighting, heat transfer, acoustic or radio-wave propagation simulations. These methods rely in most cases on a volumetric representation of the environment, with adjacency and incidence relationships. Unfortunately, many buildings data are only given by 2D plans and the 3D needs varies from one application to another. To face these problems, we propose a formal representation of consistency constraints dedicated to building interiors and associated with a topological model. We show that such a representation can be used for: (i) reconstructing 3D models from 2D architectural plans (ii) detecting automatically geometrical, topological and semantical inconsistencies (iii) designing automatic and semi-automatic operations to correct and enrich a 2D plan. All our constraints are homogeneously defined in 2D and 3D, implemented with generalized maps and used in modeling operations. We explain how this model can be successfully used for lighting and radio-wave propagation simulations.

Out of core photon-mapping for large buildings

This paper describes a new scheme for computing out-of-core global illumination in complex indoor scenes using a photon-mapping approach. Our method makes use of a cells-and-portals representation of the environment for preserving memory coherence and storing rays or photons. We have successfully applied our method to various buildings, composed of up to one billion triangles. As shown in the results, our method requires only a few hundred megabytes of memory for tracing more than 1.6 billion photons in large buildings.

Constrained Convex Space Partition for Ray Tracing in Architectural Environments

This paper explores constrained convex space partition (CCSP) as a new acceleration structure for ray tracing. A CCSP is a graph, representing a space partition made up of empty convex volumes. The scene geometry is located on the boundary of the convex volumes. Therefore, each empty volume is bounded with two kinds of faces: occlusive ones (belonging to the scene geometry), and non‐occlusive ones. Given a ray, ray casting is performed by traversing the CCSP one volume at a time, until it hits the scene geometry. In this paper, this idea is applied to architectural scenes. We show that CCSP allows to cast several hundreds of millions of rays per second, even if they are not spatially coherent. Experiments are performed for large furnished buildings made up of hundreds of millions of polygons and containing thousands of light sources.

Efficient Ray Traversal of Constrained Delaunay Tetrahedralization

Acceleration structures are mandatory for ray-tracing applications, allowing to cast a large number of rays per second. In 2008, Lagae and Dutre have proposed to use Constrained Delaunay Tetrahedralization (CDT) as an acceleration structure for ray tracing. Our experiments show that their traversal algorithm is not suitable for GPU applications, mainly due to arithmetic errors. This article proposes a new CDT traversal algorithm. This new algorithm is more efficient than the previous ones: it uses less arithmetic operations; it does not add extra thread divergence since it uses a fixed number of operation; at last, it is robust with 32-bits floats, contrary to the previous traversal algorithms. Hence, it is the first method usable both on CPU and GPU.